The Crossing of Lines
by bravevulnerability
Summary: His wedding band does a decent job of keeping things platonic between them, but while on assignment together in Brussels, feelings become even harder to ignore. Pre-canon Joan/Arthur. One shot.


They had been undercover in Brussels for nearly a week now and with nothing to show for it. Despite a scheduled meet with an asset that had gone according to plan and a brief summary of their target's possible whereabouts for the next few days, the two operatives on assignment had failed to catch an actual glimpse of their target yet.

Agent MacKenzie was less than thrilled about the setback.

Spending the week with Arthur Campbell had been nothing short of pure, torturous hell. It wasn't that they didn't get along – that was part of the problem. They got along too well.

Since the day she had met him in the DPD, Joan had always felt an attraction to her boss, and the feeling definitely was not one-sided, but the sight of the golden band on his finger always managed to quell the ever-present electricity between them. She didn't need the added stress loving a married man could potentially bring her. Besides, they both had enough on their plates without adding the complications of a forbidden relationship.

So she kept it profession, and so did he. They still teased, still flirted, did a careful dance without crossing the line that had been wordlessly drawn between them. Everything had been bearable up until the current head of DCS thought they would be the perfect pair to play a married couple for an undercover op in Brussels.

For the past week, they had been living together under false identities and the same roof in a one bedroom apartment that was far too small to keep things comfortable. It was tense, to say the least. Of course Arthur had been a gentlemen throughout the whole ordeal, sleeping on the couch every night while he insisted she took the queen sized bed in the next room, attempting to give her as much privacy as possible, and keeping conversation business related. His courtesies did little to ease the tension brought on by the close quarters though. Sleep was still made near impossible for her every night by the heavy weight of the faux diamond band around her left hand ring finger and the knowledge that he was only a few steps away in the next room didn't help either.

Tonight was their last chance to gain eyes and hopefully intel from a new potential asset the CIA had had their eyes on for a few months now and Joan swore to herself she would not allow personal feelings to affect her any longer and focus solely on the reason they had come to Brussels in the first place.

"Almost ready, MacKenzie?" Arthur called almost impatiently from the couch in the living room that he was all too familiar with. He was dressed in a sleek, black tux that he was glad he hadn't been responsible for paying for and he was awaiting his partner so they could get to the event on time and begin scouting for their asset. The sooner they got this over with, the better. "Joan, are you almost-"

"Calm down, Arthur," He heard her voice placate him as she appeared in the bedroom's open doorway.

Suddenly their assignment was the last thing on his mind.

Joan was dressed in a strapless, shimmering midnight blue ball gown that clung to her lithe figure like a second skin with a skirt that flowed open at the waist and caused her pale blue eyes to shine like sapphires. The soft blonde waves of her hair fell past her shoulders and fell in a curtain around her face when she self consciously glanced downwards and brushed a hand over the front of her dress, her red lips forming a gentle frown as he stood silent before her.

"Do you think this is okay?" she asked hesitantly and within seconds Arthur had closed the few short feet of distance between them until he was standing directly in front of her, inhaling the sweetly exotic scent of her perfume.

"Joan," he said, laying a tentative hand on the swell of her hip. "You look breathtaking."

Her breath stuttered on its way past her lips at his close proximity and the reverence that clouded his voice. He was toeing that invisible line and the last thing she wanted was for him to take a step back, like he always did. She wanted him to cross it.

Instead, she sighed his name warily and made to step around him towards the door, but he caught her wrist.

"I would have gotten you something completely different," he murmured, staring contemplatively at the wedding ring on her finger, sweeping his thumb over the gaudy diamond protruding from the sterling silver. "I would have bought you something more…delicate, subtle, but beautiful. Something that fit you better."

She blinked, entranced by the back and forth motion of his thumb over her finger and the weight of words he knew better than to speak aloud.

"Arthur," she whispered again, slowly retracting her hand from his and refusing to meet his piercing eyes as she headed towards the door, the place on her wrist still burning from where his hand had been.

* * *

The ride in the back of their town car wasn't uncomfortable, but silent. She kept her eyes on the passing city lights outside the window, and he failed to keep his anywhere but on her. When they arrived at the venue, Arthur offered his hand getting out of the car and she accepted it, held onto him even after they were inside the ballroom of the grand hotel where the black tie event that their target was said to attend.

Tonight, Joan told herself, they were different people. They were a happily married couple living in Brussels with no ex wives or dangerous missions to plague their minds, and it was their last night to play these roles, so she decided she was going to let herself enjoy it while she could.

After half an hour of mingling with fellow patrons, Arthur led her to the middle of the floor among the slew of other dancing couples and collected her in his arms. She smiled contently and laced an arm around his neck while one of his hands spanned the small of her back and the other tangled with hers.

She had only been in Arthur Campbell's arms once before, after an unforgettable mission in Nairobi that had left her more broken and vulnerable than she could ever remember feeling. It had been her first day back at Langley and he had called her into his office only minutes after her arrival. He hadn't said anything, only closed the door, checked the blinds, and enveloped her into an embrace that combatted the long settled chill in her bones with warmth. He had held her for a long time. That was the first time they had stopped pretending there was nothing between them. Being in his arms again felt like coming home.

Arthur pressed his cheek to hers and whispered, "I think I spot our target at two o' clock."

"Just keep eyes on him, don't want to spook him," she murmured, squeezing lightly on the tensed shoulder under her hand.

"He's watching us too. Shit, Joan, I think we've been made." he mumbled calmly into her ear but she could feel his body growing rigid against hers.

Joan kept her face neutral ad cupped his jaw in her palm, startling his attention back to her.

"Let's see if we can change his mind." she whispered, leaning forward and brushing her lips over his.

Arthur immediately tightened his hold on her waist, bringing her body closer until there was not an inch of space between them.

Joan nibbled playfully on his lower lip in response before deepening the kiss by instinctively seeking access to his mouth with her tongue. A quiet moan rose from the back of her throat as he kissed her, finally kissed her. They parted for air just in time to see their target making his way through the crowd towards the back entrance.

* * *

"Good work tonight," Arthur told her as they returned to their apartment later that night.

"Me? Don't be so modest, Campbell. You're the one who caught _and _turned him." she replied with a smirk across her lips and pride in her eyes.

"Couldn't have done it without you," he said, cupping her bare shoulders in the doorway. She had just slipped off her heels and stood a few inches below him now. She found she didn't mind the height difference so much. "We make a good team."

"Obviously. That's why they sent us."

The grin began to slip from her face when he started moving closer.

"Arthur," she warned.

"I can't," he sighed, dropping his forehead to rest against hers.

"I know," she sighed as well, her heart crumbling in her chest. "It's okay, I understand."

"No, Joan, I can't stop. I want – I want you. You know I want you, always wanted you."

"Arthur, you're married." she reminded him grimly, placing her hands on his chest in preparation to push him away.

"Not for long. Gina and I have been over for a while now and I think it's become painfully apparent that I'm falling in love with someone else."

She swallowed hard at the admission and met his gaze.

"Oh really?"

He nodded and kissed her cheek.

"Yes, and I've been trying to fight it, so has she, but I don't think I can stay away from her any longer. Especially after that kiss we shared tonight."

"Mmm," she hummed, giving in and allowing the smile to tug her lips upwards while he skimmed his down her jaw to her neck. "I think she would agree."

"Good. Glad we're on the same page," he murmured before claiming her mouth for the second time that night and lifting her off the ground.

She was thankful for the loose, unrestricting material of her dress as her legs twined around his waist and one of his hands slid under to grip her thigh. They managed to blindly navigate through the apartment and towards the bedroom without breaking the delicious contact of their lips until they came to the entryway.

"Joan," he breathed her name with a hint of uncertainty, a question in his eyes as they flickered from her to the bed in the middle of the room.

"No more sleeping on the couch, Arthur." she said in response and smiled as he carried her the rest of the way to their bed.

* * *

_**There just aren't enough Joan and Arthur fics out there. Apologies if any information concerning Brussels or the CIA is inaccurate, but still hope you enjoyed the story. **_

_**Thanks for reading and would love to hear from you,**_

_**x**_


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